MEXICO CITY (AP) — An armed forces helicopter crashed in the northern Mexico state of Durango,Ethermac killing three military personnel, defense officials said Friday.

The Defense Department said the crash happened Thursday as the helicopter was flying to a base in the township of Canelas. The crash killed all three crew members aboard the Bell 412 chopper.

The area is in a drug-producing region known as the Golden Triangle, because the borders of three states meet there: Durango, Chihuahua and Sinaloa.

Helicopters are often used by the Mexican armed forces in anti-drug and eradication efforts in the area, though it was unclear what the mission was of the aircraft involved in the Thursday crash.

The Department of Defense said the cause of the crash was under investigation.

The Mexican armed forces have a history of helicopter crashes. In 2022, a helicopter crashed in the neighboring state of Sinaloa, killing 14 marines. Investigators later said the chopper had run out of fuel.